Biomedical subjects

Aleksandr Bulatov

Publications and source records attributed to Aleksandr Bulatov.

6 recordsLinked to original sources

PubMed2006

Delboeuf illusion study.

In psychophysical experiments, the Delboeuf illusion was measured as a function of spatial parameters of the stimulus pattern. During the experiments, the stimulus shape, size, luminance, and the dimensions of inducing surround varied. Subjects were asked to change the size of the test part of the stimulus by adjusting its diameter to value that made the test part appear equal to the perceived size of the referent part. The difference in diameters between the test and referent parts of the stimulus, determined after the perceived equality was achieved, was considered to be the value of the illusion magnitude. The magnitude of the Delboeuf illusion was dependent on the type of the stimuli and their contrast: the filled circles with the luminance contrast yielded stronger illusion than the open circles and the stimuli with isoluminant colors. The magnitude of the illusion did not change noticeably with variations of the luminance of the stimulus, but diminished when the luminance of the stimulus approached the level of isoluminance with the background. The neurophysiological spatial filtering model, applied to the Delboeuf stimuli patterns, has provided computational results similar to the present experimental findings.

Humans↗

PubMed2005

Superimposition of illusory patterns with contrast variations.

In psychophysical experiments, a perceived length matching task was performed. The stimuli were made of two spatially superimposed illusory figures that differed in structure and luminance contrast but had the same length and coincided precisely, with their ends matched. The contrast of one of the figures was fixed, and that of the other varied. In experiments with stimuli viewed monocularly, the combined patterns produced illusions of perceived length, the strength of which varied with alterations of contrast of one of the figures. If the figures were presented separately to different eyes of the same subject, changes of contrast did not have a noticeable influence on the illusion's strength. When the two stimulus components were displaced spatially and shown side by side, the monoptic and dichoptic stimuli yielded different results as well. The illusion's strength increased with an increase of the distance between the figures when viewed monocularly, but remained invariable if the figures were presented separately to each eye. The results obtained in experiments with dichoptic stimuli suggest that stimulus length distortions may occur in the monocular retinocortical pathways.

Contrast Sensitivity↗

PubMed2005

Distracting effects in length matching.

In psychophysical experiments, subjects matched two spatial intervals of a three-spot stimulus into what appeared to them to be equal. The stimulus was flanked by stripes. The length matching errors increased in proportion to the referent interval of the stimulus and approached 6-12 percent of its length. Also, the error increased with an increase of the width of the gaps between the spots and the distracting stripes. Error reached a maximum at gaps equal to 10-15 percent of the length of the referent interval of the stimulus. When the luminance of the stripes increased or decreased, in comparison to the luminance of the background, length matching errors grew symmetrically and became approximately constant at higher contrasts. The experimental findings show the presence of local positional averaging which may be described quantitatively by means of spatial filtering procedures.

Humans↗

PubMed2005

Psychophysical measurements of illusion of the puffy circle.

The strength of an illusion of curvature created by an equilateral triangle, square or pentagon inscribed in a circle has been measured in the psychophysical experiments. The arcs of the circle looked as if they were bowed outwards in the stimuli of various sizes, but, at a fixed diameter of the circumscribed circle, the triangles produced the strongest, and the pentagons, the weakest illusion. The strength of the illusion augmented with the stimulus diameter. Concave and convex sides of the inscribed figures caused less illusory effect than the straight ones. Similar distortions of the stimuli have been observed in the output of a neurophysiological model of spatial frequency filtering of images, and the computed curves resembled those of the experimental data, in respect to their shape and quantitative values.

Adult↗

PubMed2005

[Müller-Lyer illusion and colour contrast].

In psychophysical experiments, subjects adjusted the test part of the Müller-Lyer figure to make it appear equal in length to the reference part of the figure in the absence and presence of luminance contrast. The illusion was measured as function of the length and internal angle of wings varying from 7 to 35 min of arc and from 40 degrees to 180 degrees, respectively. Müller-Lyer figures, 130 min of arc long with no shaft line, were generated by Cambrige Research Systems VSG2/3 and presented as stimuli on an EIZO T562 monitor with gamma correction. The CRT primary colors provided chromatic contrast between the stimulus and the background area. Prior to the experiments, the method of two-color gratings was used to detect isoluminance for each color pair. The experimental curves showed a significant increase of the illusion strength up to 1.5-2 times at isoluminance irrespective of the colors combined. The data obtained are interpreted in terms of spatial-frequency filtering and low-pass chromatic filters.

Color Perception↗

PubMed2003

[Stimulus symmetry influence on curvature perception].

In the psychophysical experiments the symmetrical bright lines of various length and curvature are presented against the dark background on the monitor. The subjects are asked to adjust the test-spot by moving it horizontally or vertically into the invisible arc linking the endpoints of two visible segments of the given stimulus. The data have shown that the precision of curvature estimation depended on type of the curves: it is higher for the centered circle, less for the exponential spiral and still less for the shifted circle. The precision is in direct proportion with the length of the visible segment and in reverse proportion with the invisible segment of the stimulus. The curvature estimation does not depend on the stimulus symmetry, orientation, and position in the visual field.

Adult↗